If the statement you're responding to contains a subject pronoun (omitted or not), you likewise use a subject pronoun, like 'yo'.
If the statement contains an indirect object pronoun, you respond with an indirect object pronoun, like 'a mí'.

If the statement you're responding to contains a subject pronoun (omitted or not), you likewise use a subject pronoun, like 'yo'.
If the statement contains an indirect object pronoun, you respond with an indirect object pronoun, like 'a mí'.